暂停时如何使AVPlayer重绘当前的AVItem videoComposition [英] How to get AVPlayer to redraw current AVItem videoComposition when paused

问题描述

我正在为macOS构建一个简单的视频编辑器:将电影文件作为AVAset加载，由AVVideoComposition中的一系列CIFilter转换，然后由AVPlayer播放.我为CIFilter的某些参数提供了UI控件.

I'm building a simple video editor for macOS: A movie file is loaded as an AVAsset, transformed by a series of CIFilters in a AVVideoComposition, and played by an AVPlayer. I present UI controls for some of the parameters of the CIFilters.

在播放视频时，一切正常，我滑动滑块，效果发生变化！但是，当视频暂停时，更改UI中的控件后，AVPlayerView不会重绘.

When video is playing everything is working great, I slide sliders and effects change! But when the video is paused the AVPlayerView doesn't redraw after the controls in the UI are changed.

我如何鼓励AVPlayerView暂停时重新绘制其当前项目的videoComposition的内容?

How can I encourage the AVPlayerView to redraw the contents of the videoComposition of it's current item when it's paused?

class ViewController: NSViewController {

    @objc @IBAction func openDocument(_ file: Any) { ... }

    @IBOutlet weak var moviePlayerView: AVPlayerView!

    var ciContext:CIContext? = CIContext(mtlDevice: MTLCreateSystemDefaultDevice()!)

    var sliderValue: Double = 0.0

    @IBAction func sliderMoved(_ sender: NSSlider) {
        self.sliderValue = sender.doubleValue
        // need to update the view here when paused
        self.moviePlayerView.setNeedsDisplay(self.moviePlayerView.bounds)
        // setNeedsDisplay has no effect.
    }

    func loadMovie(file: URL) {
        let avMovie = AVMovie(url: file)
        let avPlayerItem = AVPlayerItem(asset: avMovie)

        avPlayerItem.videoComposition = AVVideoComposition(asset: avMovie) { request in
            let output = request.sourceImage.applyingGaussianBlur(sigma: self.sliderValue)
            request.finish(with: output, context: self.ciContext)
        }

        self.moviePlayerView.player = AVPlayer(playerItem: avPlayerItem)
    }
}

推荐答案

事实证明，重新设置AVPlayerItem的videoComposition属性将触发该项目重新绘制.即使将属性设置为其当前值，该方法也起作用:item.videoComposition = item.videoComposition.该属性设置器似乎具有未记录的副作用.

It turns out re-setting the AVPlayerItem's videoComposition property will trigger the item to redraw. This works even if you set the property to it's current value: item.videoComposition = item.videoComposition. The property setter appears to have undocumented side effects.

要修复上面的示例代码，请执行以下操作:

To fix the sample code above, do this:

@IBAction func sliderMoved(_ sender: NSSlider) {
    self.sliderValue = sender.doubleValue
    // update the view when paused
    if self.moviePlayerView.player?.rate == 0.0 {
        self.moviePlayerView.player?.currentItem?.videoComposition = self.moviePlayerView.player?.currentItem?.videoComposition
    }
}

希望有人发现这很有用！

Hopefully someone finds this useful!

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